TEMPE, Ariz. (AP) - After their worst performance of the season, the Arizona Cardinals’ lead in the NFC West is down to a precarious one game over surging Seattle.

Drew Stanton and the Cardinals’ offense barely have a pulse. The usually stout defense was riddled for 500 yards in Arizona’s 29-18 loss at Atlanta on Sunday, a game that was not nearly as close as the final score indicated.

Now the road only gets rougher.

Up next are the Kansas City Chiefs, who are 7-5 and in the thick of the fight for at least an AFC wild card berth. At least the game is at home, where the Cardinals are 6-0 this season and 12-2 since coach Bruce Arians took over a year ago.

Arians said on Monday that the pratfall in Atlanta, Arizona’s second straight loss after a six-game winning streak, was perplexing given the great week of practice the team had put in after losing at Seattle.

“It was an outstanding week of preparation,” he said. “But you can’t play in the National Football League without passion and energy, and we brought none of the above to that game. It’s our first time in a long time. I think that some guys fell into the trap that the Falcons weren’t any good. That’s a bad trap to fall into.”

Injuries still are mounting in the desert.

Safety Tyrann Mathieu fractured his left thumb in Sunday’s game and doctors were determining how to treat it, Arians said.

“Best case scenario is put it in a cast and he can play,” Arians said. “Worst case is put a pin in it and out for three weeks.”

Right guard Paul Fanaika and left tackle Jared Veldheer have ankle sprains and their prospects for next Sunday are uncertain.

But there is some good news on the injury front. After missing two games with a bruised knee, eight-time Pro Bowl wide receiver Larry Fitzgerald should practice Wednesday, Arians said. The team also gets outside linebacker Matt Shaughnessy back. Shaughnessy had been on the injured but eligible to return list for the last eight games.

Arians said he wouldn’t yell at the players in their Monday meeting.

“I’m just honest,” he said. “When you stink, you stink. You point out how you stunk and get it corrected.”

Besides, he said, “the tape is so bad it speaks for itself.”

Drew Stanton dropped to 3-3 as a starter, 1-2 since Carson Palmer went down with a season-ending knee injury. The offense went more than 11 quarters, 28 consecutive possessions, without scoring a touchdown before it finally got one late against the Falcons.

Cornerback Patrick Peterson acknowledged that the defense has to step up with Palmer out, something that certainly didn’t happen in Atlanta.

“We still have all the confidence in the world in Drew but we’re still playing with a backup quarterback,” Peterson said. “That changes the dynamics of everything.”

Tight end John Carlson defended his quarterback.

“It’s certainly not Drew’s fault,” Carlson said. “Every individual on the offensive side of the ball needs to play better, needs to execute better.”

Arians said Stanton was “really, really hot and cold” against the Falcons, when he threw two interceptions.

“Threw the ball extremely well outside and down the field, and then overthrew Jaron (Brown) six inches too high on the interception,” Arians said. “The other (interception) he went through his progressions and then just dumped one over Michael’s (Floyd) head. Those are critical errors, and he has not made those earlier in the season, something that’s easily corrected.”

Kansas City is coming off a one-sided home loss to Denver and is fighting for its playoff life.

The Chiefs, Arians said, will not be an easy foe for an Arizona team that has to stop its slide or see a remarkably successful season slip away.

Peterson, who talked last week about how he wanted to go against Julio Jones, was torched by the Atlanta receiver, who caught 10 passes for a career-high 189 yards. He said he always talks that way about an opponent’s best receiver and any talk about him “calling out” Jones is “baloney.”

The Cardinals aren’t in the position to call out anybody.

“We’ve got to get back to what got us here,” Peterson said.

NOTES: The Cardinals released linebacker Desmond Bishop and elevated guard-center Anthony Steen from the practice squad.